How To Use A Sleep Calculator To Find Your Perfect Bedtime

August 20, 2017 |

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Sleep experts always seem to recommend going to bed much earlier than most people would like or can. Even then, it's not guaranteed that you'll sleep through the night. Getting a good night’s sleep starts with knowing when to go to bed. If you’re not sure when that is, the sleep cycle calculator can be your guide. It works by telling you when you need to go to sleep based on what time you need to wake up. Here’s how to use a sleep calculator to find your perfect bedtime so you can wake up ready to go.

What is the Sleep Calculator and How Does it Work?

A sleep calculator is an online tool you can use to tell you when you should go to bed based on what time you need to wake up in the morning. It works by calculating your nightly sleep through a series of 90-minute sleep cycles so you can fall asleep as soon as one begins and wake up as another finishes. The goal is to calculate a formula that allows you to sleep through as many 90-minute sleep cycles as possible, so you don’t wake up in the middle of one.

Most adults sleep through approximately five or six 90 minute sleep cycles each night. When you wake up in the middle of one, you may feel groggy and have trouble concentrating during the day. The sleep calculator bases its calculations off a 15 minute grace period when you first go to bed, which is the amount of time it takes most adults to fall asleep. Then it creates a series of specific times for you to choose from, so you don’t wake up in the middle of a cycle.

For example, if you need to wake up at 8 am, the sleep calculator advises you to go to bed at 10:45 pm or wait until the next sleep cycle begins at 12:15 am. The creators behind the calculator explained that getting proper rest is more than just going to bed early. It’s about sleeping through as many sleep cycles as possible based on the body’s natural rhythm.

Researchers suggest that when you wake up during the wrong sleep cycle stage, such as slow-wave or REM sleep (when dreams occur), you will feel more tired than when you went to bed in the first place. This theory is known as sleep inertia, and it’s such a big deal that researchers are told not to wake test subjects when they are in REM sleep (1).

bedtime calculator

How Is Your Sleep Cycle Measured?

The sleep calculator bases its formula on the information it receives from a brain study test called a polysomnography. It is used to measure several important factors during sleep, such as blood oxygen levels, brain waves, breathing, heart rate and leg and eye movements. According to the American Academy of Sleep Medicine, there are four different stages of sleep:

  • N1 (non-REM)
  • N2 (non-REM)
  • N3 (non-REM)
  • REM

Only one of the four sleep cycles contains REM sleep. During a night of sleeping, you continuously move through these four cycles. When you move from N1 to N3, the polysomnography shows that your brain waves become larger and lower in frequency. This is known as slow-wave sleep, or deep sleep (2).

Healthy adults usually begin their sleep cycle with non-REM sleep. Transitioning to the N1 sleep stage occurs within seconds once you first begin to fall asleep. The N1 sleep stage only lasts for approximately one to seven minutes. The next stage, N2, lasts approximately 10 to 25 minutes. As N2 sleep continues, N3 sleep begins to set in by increasing high-voltage and slow-wave activity in the brain. The last stage of non-REM sleep lasts 20 to 40 minutes and is especially hard to wake a person from (3).

Every 90 minutes, a person moves into REM sleep, which is characterized by paralysis of the muscles as well as the random movement of the eyes (1). According to the sleep cycle calculator, waking up in the middle of this process of deep sleep means you’ll be extra tired and irritable.

Who Should Use The Sleep Calculator?

The sleep calculator has gotten mixed reviews from many different sources. Some reviewers claim it doesn’t work at all and is a complete waste of time. Others credit it for giving them the best sleep of their lives when nothing else has worked.

Using a sleep calculator may be a good idea for those who still want quality sleep but aren’t a fan of going to bed early. According to the sleep calculator principles, you can still get good sleep on less than eight hours if you catch the right sleep cycle. If you’ve ever noticed that you feel worse when you get too much sleep, you might benefit from a calculated sleep formula.

Research shows there are a few fundamental flaws with the sleep calculator. First, not everyone experiences a perfect 90-minute sleep cycle, which would make the sleep calculator completely useless for some. According to a 1979 study, approximately 70 percent of subjects had sleep cycles that were as much as 20 minutes shorter than average times (1). The remaining 30 percent of subjects had sleep times that were longer (1). If the sleep calculator were based on this study alone, it would not work.

Additional research shows that the typical sleep cycle is made up of slow-wave sleep for the first half of the night and REM sleep makes up the second half. Because no two sleep cycles are the same, it’s hard to use a formula that meets everyone’s needs based on a 90-minute cycle. For example, two people could be matched to the same ideal sleep times, but their inner sleep cycles could be hours off.

Your nightly sleep also depends on how well you slept the night before. Research shows that the slow wave sleep in stage N3 can be made up if it’s missed. So if you normally have 100 minutes of N3 sleep each night and you miss one night of sleep, you’ll make up for it the next evening. So using a sleep calculator wouldn’t work in this scenario either.

Finally, not everyone falls asleep within 15 minutes of going to bed. Some people snooze as soon as their head hits the pillow while others take much longer. The sleep calculator doesn’t account for this adjustable time.

Keep in mind that everyone has a unique sleep cycle that doesn’t respond to a one-size fits all sleep plan. Despite a few flaws, the sleep calculator can be a beneficial tool to help you regulate your sleep levels based on the needs of the average person. If you don’t suffer from a sleep disorder and you are looking to increase the quality of your sleep, catching the beginning of a sleep cycle could work for you.

How To Use The Sleep Time Calculator

Many sleep calculators are available for free on the internet. You can find them by doing a basic Google search. Below are some examples:

You can also find a sleep calculator app for your phone, but some of them may cost money. It might be a good idea to try a sleep calculator on the internet for free and then download an app to your phone if it works for you. Here are some examples:

To use your sleep calculator, enter the time you need to wake up. The sleep calculator will then calculate what time you need to go to bed. Some sleep calculators give you the option of calculating what time you should wake up if you were to go to bed immediately.

A person’s sleep needs change throughout their lifetime. If you are using the sleep calculator for a child, keep in mind that the times will be different than for an adult. Here is an easy guide to help you determine how many hours you should get a night based on your age.

  • Newborns (0-3 months): 14 to 17 hours a night/day
  • Infants (4-11 months): 12 to 15 hours a night/day
  • Toddlers (1-2 years): 11 to 14 hours a night/day
  • Preschoolers (3-5): 10 to 13 hours a night
  • Grade school aged children (6-13): 9 to 11 hours a night
  • Teenagers (14-17): 8 to 10 hours a night
  • Young adults (18-25): 7 to 9 hours a night
  • Adults (26-64): 7 to 9 hours a night
  • Older adults (65+): 7 to 8 hours a night

If you decide to aim for eight hours of sleep, count backward from the time you need to wake up to determine approximately what time you should go to bed. For example, if you need to wake up at 6:00 am, and you want to get around seven to nine hours of sleep, your bedtime options based on the sleep calculator are 8:45 pm or 10:15 pm.

Tips To Assist Your Sleep Calculator Reading

Even if you’re using the sleep calculator, it’s a good idea to prepare for bed mentally. If it takes you longer than 15 minutes to fall asleep, it could miscalculate the entire formula, which makes using a sleep calculator pointless. To assure that you will fall asleep within the 15-minute time frame, consider following these three tips:

1. Develop a bedtime routine.

To help make the sleep calculator more useful, try adopting a bedtime routine that makes you tired enough to fall asleep within 15 minutes. A bedtime routine helps you physically and mentally prepare for sleep. After dinner, try doing a relaxing activity for two to three hours until it’s time for bed, such as yoga, meditation, reading a book or journaling.

Don’t take negative thoughts to bed with you by making a conscious effort to stop worrying about work or other stressful events after 6 pm.If it’s nice out, grab a cup of herbal tea and sit outside to watch the sunset. Stay away from electronics or anything stimulating that could keep you awake.

2. Make your mornings bright and keep your nights dark.

Syncing your sleep cycle is an important part of regulating your melatonin levels. Melatonin is a hormone produced in the pineal gland of the brain. At night when the sun goes down, the pineal gland begins to produce melatonin and releases it into the bloodstream to make you sleepy. Melatonin levels stay elevated for up to 12 hours until the next morning when you are exposed to light. During the day, your melatonin levels are hardly measurable (3).

Turning off all lights at night when you’re ready to go to bed can help stimulate melatonin production. Similarly, when you wake up and need to get moving, sunlight can help reduce melatonin levels, so you feel more alert. Using a sleep calculator can help you naturally sync this process so that eventually you don’t need help falling asleep.

3. Eat a light dinner several hours before bed.

To get in as many 90-minute sleep cycles as you can, try to eat a light meal several hours before going to bed. It’s hard to fall asleep when your digestive system is busy trying to break down a large meal. Aim for four to six smaller meals throughout the day to take a load off your digestive track. Stick to water at dinner as alcohol and caffeinated drinks could keep you awake.


It’s also a good idea to make sure your last meal is eaten a few hours before you lay down. Although your digestive track keeps working all night long, it could keep you awake if you burden it with too much food. A heavy meal or too many beverages may cause you to wake up in the middle of the night with the urge to use the bathroom.